The sterilization or germ reduction in liquid media in many processes is an important method step. Contamination with active, i.e. capable of reproduction, biological materials such as microorganisms or viruses often poses a risk to product safety which has to be countered effectively. There are also applications in which the contaminants themselves are the product and their inactivation is a desired product modification. Examples of such products are specific vaccines.
Germ reduction by inactivation using ultraviolet radiation, in particular with UV-C radiation and specifically at 254 nm has been known for a long time and has many practical applications. An example, in addition to surface sterilization, is also the treatment of liquid media such as drinking and waste water.
It is a considerable technical challenge if, besides the germs to be inactivated, materials of value are also present which, to a certain degree, can also be damaged by the radiation. Such requirements are typical for sterilization in the field of foodstuffs and of pharmaceutical active substances, such as proteins. Additional difficulties arise when the clouding of the processed liquid in the range of the UV-C radiation is high and thus the penetration depth of the inactivating radiation is low. Such applications require technical systems which can realize, despite the high clouding, a homogeneous irradiation, that is to say a dense dose distribution. In apparatuses through which fluids flow, a certain residence time, synonymous with irradiation time, should additionally be envisaged here. The system-specific residence time distribution here leads to a broad, i.e. inhomogeneous, dose distribution in the liquid.
In order to solve these problems, the prior art discloses various possibilities for transverse mixing in irradiated apparatuses through which fluid flows. The simplest solution, the production of a turbulent flow, may indeed result in a good transverse mixing, but is often difficult to realize in practice since the required high liquid speed together with the necessary irradiation time leads to impracticably long apparatuses. One solution in slow, laminar flow here envisages the fitting of mixing elements in the flow-guiding system [U.S. Pat. No. 6,190,608, EP Patent 0910417]. The internals (static mixers) are used to forcibly mix the laminar flow. Another solution makes do without internals: a helical flow-guiding system induces secondary flows which result in the desired transverse mixing. This flow-technological effect is known from the literature [VDI-Wärmeatlas (VDI Heat Atlas), Chapter Gc, Springer Verlag, Berlin Heidelberg 2002] and is described as the solution for said application [WO 02/38502, WO 02/38191, EP 1464342]. In a particularly preferred form, a tube with helical profile is applied in a form-fitting manner onto a quartz glass tube. This results in a module with a helical channel which can be irradiated from the inside by way of the quartz glass tube.
It is a disadvantage of the solutions according to the prior art that they can be cleaned only with difficulty. Cleaning the apparatuses, specifically the irradiation modules, is an important requirement for bulk products, for example in the foodstuff field where repeated use of the modules must be ensured for economic reasons. In the case of high-price products, such as pharmaceuticals, a lack of cleanability is countered by the concept of disposability in irradiation modules.
Cleaning can in principle take place by a cleaning liquid flowing through the entire apparatus or by mechanical or chemical cleaning of the parts after disassembly. The solutions with internals additionally have, because of them, an increased tendency to soiling and are therefore, from the viewpoint of cleanability, inferior to the helical tube modules according to the prior art. In the helical tube modules in which all components are connected in as form-fitting a manner as possible in order to enable optimum flow-guidance, disassembly and reassembly of the parts is not possible. According to the prior art, thus only cleaning by way of a cleaning liquid flowing through is possible. This is possible by its very nature not during but only after processing. In addition, the purely chemical cleaning is significantly less effective as compared to the mechanical or mechano-chemical cleaning, in particular when deposits form on the module walls. Chemical cleaning agents themselves are additionally mostly harmful for the subsequent applications. This results in a module having to be freed, after cleaning, from the cleaning agent, too, for example by flushing with water.
It was therefore an object of the invention to develop an irradiation module for the irradiation of fluids, which does not have the abovementioned disadvantages.